Victorian taxpayers could be on the hook for an extra $16 billion to build and run the Suburban Rail Loop, with independent analysis projecting the cost to blow out to $216 billion.
The 90km orbital rail line is Victoria's most expensive infrastructure project, designed to run from Cheltenham in Victoria's southeast to Werribee in the southwest via Melbourne Airport.
The first two stages, SRL East and North, will cost an extra $9 billion to build and maintain and $7.5 billion to run over the next 50 years, according to Victoria's independent Parliamentary Budget Office.
The analysis, requested by the state opposition, is an update to its 2022 report that calculated construction and operational costs for the first two stages at $200 billion.
The 26km SRL East running from Cheltenham to Box Hill, which began early works in 2022 and is expected to open in 2035, is predicted to cost $32.8 billion to build.
The budget office predicts it will cost an extra $51 billion to operate until 2084.
The second stage of SRL North, running from Box Hill to Melbourne Airport, is forecast to have a price tag of $63 billion to build and cost $69 billion to operate.
The $216 billion cost estimate does not account for the final phase, which incorporates a line from Werribee to Sunshine and a long-waited route to the airport.
Suburban Rail Loop was unveiled by the Andrews government as a major 2018 state election policy, with an initial estimated price tag of $50 billion for the entire rail line.
A 400-page business and investment case released in 2021 showed the east and northeast sections could cost up to $50.5 billion.
The government has pledged $11.8 billion to build the eastern section, with the other two-thirds of funding slated to come from the Commonwealth and "value capture" revenue.
But the Albanese government has only committed $2.2 billion to the project so far.
Opposition Leader John Pesutto said the latest analysis should be a wake-up call to stop the project.
"It will cost a bomb," he told reporters on Wednesday.
"No government can seek a mandate when the mandate it sought was based on fraud ... it lied about the cost, it lied about the cost-benefit analysis, it lied about the business case."
The state Liberal leader argued operating costs should be taken into account in price estimates and said the opposition would provide estimates in that way moving forward.
Transport Infrastructure Minister Danny Pearson suggested the Liberals had asked a "dodgy" question to produce a misleading answer.
He noted the budget office's costing to build SRL East was in line with the government's estimated range of $30 billion to $34.5 billion, but sought to discredit its projection for the northern section.
"I reckon they've got out the tape measure," Mr Pearson said.
"They looked at the distance of SRL East, then they looked at the distance of SRL North (and) said 'it's basically double the size, therefore it's double the cost'."
The budget office estimate does not include any offsets to costs from farebox revenue from increased passenger trips.
Mr Pearson claimed the analysis of operating expenses incorrectly included drivers, despite the business case noting rail loop trains would be driverless.
